1. Field of the Invention
This invention relates to a diode, more particularly, a pin diode for transducing incident rays to an electrical signal, a producing method thereof, and a contact image sensor device comprising the same for sensing an image of objects.
2. Description of the Related Art
In a pin diode, if a part of an incident layer, e.g., an n layer, is microcrystallized, the n layer would have a higher optical transparency and improved light sensitivity, and would have a higher electrical conductivity due to a lower electrical resistance of a microcrystalline silicon than that of a hydrogenated amorphous silicon, and therefore the diode characteristics of the pin diode would be improved (Y. Uchida, et al., "Microcrystalline Si-H Film and Its Application to Solar Cells", Japanese Journal of Applied Physics, vol. 21, No. 9, 1982, pp 586-588).
Accordingly, the aforementioned pin diode and a contact image sensor device comprising this pin diode could have improved conversion efficiency in a photoelectric conversion.
A method for microcrystallizing the incident side of a pin diode, e.g., the n layer, wherein a temperature of a deposited substrate Ts is kept between 500.degree. C. and 600.degree. C. during deposition of each layer, is described in "F. Morin, et al., Polycrystalline silicon by glow discharge technique, Applied Physics Letters, vol. 35, No. 9, 1979, pp. 686-687". According to this method, the n layer does not become hydrogenated amorphous silicon, but becomes a microcrystallized amorphous silicon. However, since hydrogen included in the hydrogenated amorphous silicon in a p layer and an i layer is missing in aforementioned high substrate temperature Ts, defects in the hydrogenated amorphous silicon are remarkably increased and the diode characteristics (e.g., rising characteristics of ON current in a forward direction and a leakage current value in a reverse direction) of the pin diode are remarkably degraded.
A deposition method, in order to microcrystallize a whole layer at a low deposition substrate temperature Ts of about 250.degree. C. which is a usual deposition temperature of hydrogenated amorphous silicon, is described in "Y. Osaka, et al., Microcrystalline Silicon (.mu.c-Si) Prepared by Plasma-Chemical Techniques, JARECT vol. 16, Amorphous Semiconductor Technologies & Devices, 1984, pp 80-91". In this method, high power (e.g., more than about 0.2 W/cm.sup.2) is applied between an anode and a cathode in a reaction vessel and mono-silane supplied as a raw gas is diluted with hydrogen (e.g., hydrogen:mono-silane =1:1). According to this method, since a depositing surface of the layer is covered with hydrogen and high power is supplied, microcrystallization is facilitated. However, the aforementioned high power damages the i layer which is a lower layer, and therefore the diode characteristics are remarkably degraded.